Method for dewatering and a dewatering apparatus

ABSTRACT

This invention relates to a dewatering apparatus, in particular a paper machine or a paperboard machine, for the adjustable, and controllable dewatering of a fibrous material, which is conveyed as a fibrous web that can be divided into at least two zones arranged side by side in a cross direction (CD). The dewatering apparatus is characterized in that the dewatering of the fibrous material is adaptable to a dewatering curve defined in a machine direction on the basis of measurements of the water weight of the fibrous material taken by at least two water weight sensors, in particular a one-dimensional or multi-dimensional sensor arrangement of water weight sensors, which are assigned to a zone and arranged preferably in pairs in mutually offset position in the CD direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dewatering apparatus, for a paper machine or a paperboard machine, for the adjustable, in particular controllable dewatering of a fibrous material which is conveyed as a fibrous web.

2. Description of the Related Art

Dewatering apparatuses and methods for adjusting the dewatering of a fibrous material that is conveyed as a fibrous web, in particular on a belt-shaped mesh, are used in particular in the paper industry. On account of the continuous dewatering of the fibrous material in the machine running direction, called MD direction for short, a paper machine or a paperboard machine can be regarded essentially as a dewatering apparatus for the fibrous material. The machine running direction usually designates, as in this publication, the direction in which the fibrous material is moved during the paper production process on the paper machine or paperboard machine.

At the headbox the consistency of the fibrous material in the cross machine direction (CD), meaning in the direction at right angles to the MD direction, as a rule the running direction of the fibrous material, is first pre-adjusted usually by dilution water. A headbox working with dilution water is referred to as a dilution water headbox. Consequently there can arise, in particular in the wet section of the paper machine or paperboard machine, deviations of the dewatering in CD direction of the fibrous web from a dewatering curve defined in the MD direction in particular for the overall width of the fibrous web. Said deviations in dewatering lead as a rule to deviations of the gsm substance in CD direction of the furnace-dry paper. Such deviations have a negative impact on the transverse formation profile in particular in the CD direction—which is therefore referred to as the CD profile for short—and are therefore unwelcome.

In spite of the consistency of the fibrous material being adjusted by dilution water at the dilution water headbox, the problem often arises in the MD direction, but in particular also in the CD direction, of unsatisfactory formation profiles, in particular unacceptable CD profiles, arising for example due to uneven dewatering on the mesh.

After the fibrous material is applied onto the mesh, said material continuously loses water due to gravitation or additional vacuum extraction with the help of dewatering elements, with the result that the water weight of the fibrous material on the mesh decreases continuously in MD direction. The forming of the fibrous material into paper, meaning the forming of a sheet, is thus enabled. The dewatering of the fibrous material or the forming paper continues also in the subsequent sections of the paper machine or paperboard machine, for example in the pressing section and drying section.

Known from WO 99/55959 A1 is an apparatus and a method for sheet measurement and control on paper machines and paperboard machines. The publication describes among other things the measuring of CD profiles, in particular water weight profiles in the CD direction of the paper machine or paperboard machine, with the help of water weight sensors. A water weight sensor is described which can be arranged underneath the mesh and used to measure three properties of a material, in particular the fibrous material on a paper machine or paperboard machine. Those properties are the conductance or resistance, the dielectric constant and the distance of the material from the water weight sensor, whereby one, or more than one, of these properties dominates depending on the material. The response time of such a water weight sensor lies at approx. one millisecond.

Through the arrangement of the water weight sensors in the CD direction the CD water weight profile is obtained instantaneously, as the result of which the MD changes and CD changes can be determined essentially in isolation. Cited in the prior art as points of action for the control system are the raw material supply rate at the beginning of the wet section, controlling the steam quantity in the drying section or varying the roller contact pressure in the pressing. Possibilities of actions at numerous actuators, which are controllable independently of each other in open-loop or closed-loop mode and extend in each control range over the width of the fibrous material, are cited. For example, the headbox and the steam generating system with numerous steam actuators for controlling the quantity of heat applied onto the individual zones across the sheet are cited. A similar situation exists in the calender section where segmented calender rolls have several actuators for controlling the roll contact pressure which is applied onto the sheet between the rolls in individual zones in the CD direction. By evaluating signals from scanners the control system can adjust the actuators automatically in the CD direction. Factors for uneven dewatering in the CD direction, which ultimately are responsible for fluctuations in the CD profile of the paper, are the irregular provision of fibrous material at the headbox, the clogging of openings in the woven plastic mesh, differences in the mechanical tension of the mesh, and unbalanced vacuum extraction. The fact that the MD changes and CD changes take place essentially in mutual isolation represents a certain disadvantage.

Accordingly, paper properties are currently measured in the wet section with only spot measurements or one-dimensional sensor arrays in the MD direction or the CD direction. Other known applications are traversing measurements or fixed, stationary measurements in the drying section. A clear-cut assignment of MD and CD variations is impossible with these known arrangements.

EP 1 624 298 A2 describes a microwave water weight sensor and a method for measuring the water weight in a forming section of a paper machine or paperboard machine using microwaves. The sensor generates a microwave field which penetrates partly into the material to be measured. The field is generated either with the help of a microwave transmission device, which is embedded in a ceramic film, or by way of a transmission antenna and a reception antenna, which are coupled to the microwave field through the material.

The dielectric constant of the material all around the transmission device or in the space between the transmission antenna and the reception antenna affects the wave propagation speed. The measurement is based either on the propagation time or on the phase or the phase displacement or the phase shift.

It is also possible to use a separating line resonator. The resonator measures essentially the wave propagation speed in the resonating structure. The operating frequency is selected such that it lies significantly below the relaxation frequency of water (approximately 22 GHz). The preferred frequency lies between 1 and 3 GHz, but other frequencies are also possible. The sensor can measure the water weight in the forming section of the paper machine or paperboard machine. In particular the sensor can be used both upstream and downstream from the drying section. It can also be used in double-belt forming sections.

The sensor signal is strong enough to take one-sided measurements. In addition the sensor permits multi-sensor configurations for measuring the water weight simultaneously at various positions in the CD direction of the machine in order to produce a non-sequentially scanned measurement profile. Several sensors can be arranged such that they form a sensor arrangement or a sensor field in the CD direction and/or in the MD direction. Sensor fields arranged in the MD direction can be used advantageously for determining dewatering profiles.

The sensor makes use of the fact that the dielectric constant of the fibrous material in the forming section is affected mainly by the water, which has a high relative dielectric constant of around 80 at room temperature up to frequencies of several GHz.

The publication also describes a method for monitoring a layer of fibrous material on a production line, whereby the fibrous material layer is penetrated by microwaves which have a frequency lower than the relaxation frequency of water and whereby measurements are taken of an effect which the fibrous material layer has on the microwaves. Such a sensor can be used for the present invention. The disclosure concerning the sensor is incorporated in all points into the description of the present invention.

EP 0 972 882 A1 describes a measurement system for measuring certain properties of a material web, for example, in particular a fibrous web on a paper and/or paperboard machine or a coating machine, by at least one stationary cross profile measuring device with at least one radiation source for irradiating the material web in several defined different wavelength ranges and at least one sensor for measuring the intensity of a radiation affected by the material web, and by at least one electronic meter and/or analyzer, whereby only one of the defined different wavelength ranges of the radiation is recorded preferably by one respective sensor at a certain time.

The paper industry has a need for methods which permit the production of paper with a formation profile which is as uniform as possible both in the MD direction and in the CD direction, meaning a formation profile which corresponds to a flat desired profile defined over the entire fibrous web, and for dewatering apparatuses, in particular paper machines or paperboard machines, which implement such methods.

SUMMARY OF THE INVENTION

This invention relates to a method for adjusting, in particular controlling the dewatering of a fibrous material on a dewatering apparatus, in particular a paper machine or a paperboard machine, whereby the fibrous material is conveyed as a fibrous web that can be divided into at least two zones arranged side by side in the cross machine direction.

An exact measurement of the cross profile of certain properties is possible. Measurement is possible also at relatively inaccessible points and even in regions of closed conveyance in which the material web in question is supported, for example, by a roll, a belt, a mesh and/or a felt. It is possible to record, for example, with a sensor, a radiation which is reflected from the material belt or its covering. In addition or alternatively it is also possible to record by way of a sensor a radiation which passes through the material belt or its covering.

It is proficient to provide for at least two stationary cross profile measurements set apart from each other in the MD direction. In this case it is advantageous for at least two stationary cross profile measuring devices, which are set apart from each other in the MD direction, to be assigned respectively to at least one unit such as the pressing section, the drying section etc. of the paper and/or paperboard machine or coating machine.

With a view to short control times it is recommended in EP 0 972 882 A1 to arrange, respectively, at least one stationary cross profile measuring device directly upstream and/or directly downstream from at least one actuator or actuating element affecting the respective cross profile.

The measuring system enables, respectively, at least one stationary cross profile measuring device to be provided, at least in the pressing section and/or drying section of a paper and/or paperboard machine. Alternatively, or in addition, it is also possible for at least one such stationary cross profile measuring device to be provided in the mesh section and/or at the end of a paper machine and/or a paperboard machine.

Filtering arrangement can be provided in order to filter out certain interference variables and/or the influence of at least one actuator or actuating element on the respective cross profile.

At least one stationary cross profile measurement can be configured for the quantitative recording of the gsm substance, moisture, thickness, specific constituents and/or other properties of the material web.

In particular for measurement in regions of an open web draw it is possible to provide for a respective stationary cross profile measurement with at least one optical radiation source. The sensors described in EP 0 972 882 A1 can also be used to advantage in the present invention.

The inventive dewatering apparatus for the adaptable, in particular controllable adjustment of the dewatering of a fibrous material is based generically on a dewatering apparatus, for a paper machine or a paperboard machine on which the fibrous material is conveyed as a fibrous web that can be divided into at least two zones arranged side-by-side in the CD direction.

According to the invention the dewatering of the fibrous material is adjustable advantageously to a dewatering curve defined in the MD direction on the basis of measurements of the water weight of the fibrous material taken by at least two water weight sensors which are assigned to a zone and arranged preferably in pairs in mutually offset position in the CD direction. This results, advantageously, in a saving of energy and an increase in production. In addition there is an improvement in the formation of the paper, which results in turn in an improved strength and printability of the paper. Through the inventive dewatering apparatus it is possible to keep the number of necessary sensors advantageously low.

The dewatering of the fibrous material takes place “on the basis of” measurements of the water weight taken by the water weight sensors arranged in mutually offset position, as described above, meaning that the sensor measurements are drawn on, albeit not exclusively, for adapting the dewatering adjustments. Instead of “on the basis of” you could also say “due to”. The important thing is that a causal relationship be constituted between the measurement on the one hand and the adjustment on the other hand. The causal relationship can be formed in very different ways, for example, by a classic analog control system but also by a digital, in particular very simple comparative control system or by fuzzy logic systems or by artificial neural networks etc. Even networking with a different system type, for example, a knowledge-based system, in particular with a statistical process control system, is a fundamentally conceivable and possible configuration of the causal relationship.

The dewatering can take place “in accordance with” the measurements of the water weight taken by the offset water weight sensors. Instead of “in accordance with” you could also say “in line with the level of”. This should give expression to the fact that the specific level of the measurements, meaning the measurements according to their (calibrated) value, are channeled, albeit not exclusively, into adapting the adjustment of the dewatering. If the adaptation takes place in accordance with the measurements, this signifies a value-related causal relationship such as an in particular microprocessor-assisted calculation, for example with filtering, smoothing, averaging, statistical evaluation etc.

The dewatering apparatus has at least two machine elements which are respectively zonally adjustable and are arranged in a mutually offset manner to each other in the MD direction. The elements can be, for example, foils, suction boxes, pressing-on elements in connection with a second opposing mesh or a headbox. Foils can be constructed more economically than foil strips. The foil or foil strip is used for dewatering, for example by means of turbulence. Dewatering elements can be arranged in particular in a wet section of the dewatering apparatus. According to the present invention the dewatering performance of the dewatering elements are zonally adjustable on the basis of, in particular, in accordance with, the measurements taken by the water weight sensors. Adjustment to the optimum operating point of the dewatering elements is thus achieved. In the case of suction boxes a vacuum optimization of the suction boxes is now possible.

The water weight sensors and the dewatering elements are arranged in alternating succession in the MD direction. Hence it is possible to determine in near real-time the effect of the zonal dewatering performance of a dewatering element.

According to the invention the dewatering is zonally adjustable by means of at least one forward-coupled control circuit or a “feedforward” system. If you consider a zonal dewatering deviation detected by a sensor arrangement arranged between a first and a second dewatering element, then the feedforward control system can control the zonal dewatering performance of the second dewatering element (in the MD direction) advantageously such that the second dewatering element eliminates the deviation which had previously occurred and was carried forward.

The dewatering is zonally adjustable by at least one backward-coupled control circuit.

In the case of a feedback system, the zonal dewatering performance of the first dewatering element (in the MD direction) is adjusted advantageously such that consequently the deviation does not occur at all or only to a reduced extent. The control effort for an existing feedforward control system can be lowered, advantageously, as the result.

The feedforward control system can be regarded as a cascaded or additional control system which, compared to a simple feedback control system, creates an improvement in the quality of the fibrous material formation through a further reduction of ACTUAL/DESIRED deviations. The stability of such a control cascade must be taken into account or configured accordingly.

If forward and backward-coupled control circuits are available simultaneously, which is considered a particularly favorable version, then you can speak of a distributed control system, in particular a control system acting in more than one direction, namely a control system acting at least in forward and backward direction in relation to the MD direction.

The dewatering elements are arranged, in at least one section of the dewatering apparatus. They can be arranged favorably in, or in a region of, a steam blow box or a press or a headbox, in particular a dilution water headbox. In addition, the dewatering performance can be influenced by an adjustable suction force and/or an adjustable layer thickness and/or the preferably adjustable consistency of the fibrous material emerging from the headbox and/or a preferably adjustable pressurization of the fibrous material by an opposing element and a second mesh. Through the adaptation or control of dewatering elements, in particular of different types of dewatering elements, in different sections of the dewatering apparatus it is possible to achieve a particularly exact control of the overall process near the predefined dewatering curve in the MD direction.

The dewatering performance of a dewatering element in a zone is measured at a certain time by at least one water weight sensor. The measurement point of the water weight sensor in the MD direction is in this case advantageously freely selectable. The positioning of sensors both within one section and in different sections can thus be selected or fixed advantageously in accordance with the requirements of the overall process. In this way it is possible to determine a measurement-based picture of the entire fibrous web while still having to arrange only a manageable number of measuring sensors.

At at least one measurement point, looking in the MD direction, there are favorably at least two water weight sensors per zone arranged in a mutually offset position in the CD direction. Alternatively, there can also be a one-dimensional sensor arrangement, which has more than two sensors and is orientated in the CD direction, or there can also be a multi-dimensional sensor field. In such a sensor arrangement, or sensor field, it is possible for the sensors to be configured in an integrally interconnected fashion. Through this rather more opulent equipment arrangement it is possible to measure the dewatering more informatively than with embodiments equipped with fewer sensors.

The measurements of at least a part of the water weight sensors, which are arranged in offset position in the MD direction and are assigned to a zone, are averaged. The averaging produces a slurred, or you could also say blurred, signal. The signal is zonally averaged. You could also say that the signal is received zonally slurred or blurred. Instead of averaging you can also speak of filtering or smoothing. In conjunction with the offset arrangement of the sensors it is possible to calculate, advantageously, the water curve (ACTUAL) from the zonally averaged or filtered or smoothed signal. As a further consequence the ACTUAL curve can be adapted to the DESIRED curve of the dewatering diagram.

Furthermore, a more exact image of the dewatering characteristic in the CD direction and/or in the MD direction can be determined through a suitable interpolation of measurement values from the offset water weight sensors.

In addition the present invention relates to a method for adjusting, in particular controlling the dewatering of a fibrous material on a dewatering apparatus, in particular a paper machine or a paperboard machine. The dewatering apparatus or the paper machine or paperboard machine can be configured in accordance with the present invention as described herein. The fibrous material is conveyed as a fibrous web that can be divided into at least two zones arranged side by side in the CD direction.

With the inventive method the dewatering of the fibrous material is adaptable to a dewatering curve defined in the MD direction on the basis of measurements of the water weight of the fibrous material taken by at least two water weight sensors, in particular sensor arrangements of water weight sensors, which are assigned to a zone and arranged preferably in pairs in mutually offset positions in the CD direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous properties and embodiments of the invention will be described with reference to the drawings explained below. In the drawings:

FIG. 1 shows a side view of a first embodiment of an inventive dewatering apparatus of the present invention, namely the wet section of a paper machine or paperboard machine, with dewatering elements and water weight sensors arranged underneath the long mesh;

FIG. 2 shows a plan view of the fibrous web, with a dotted-line indication of the zones;

FIG. 3 shows a plan view of the wet section of the first embodiment for clearer presentation of the mutual offsetting of the water weight sensors in accordance with the present invention; and

FIG. 4 shows a plan view of the wet section of a second embodiment of an inventive paper machine or paperboard machine; the mutual offsetting of the water weight sensors being configured differently.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures there is described below a first embodiment of an inventive dewatering apparatus 1, which in this case is a paper machine or paperboard machine. The paper machine or paperboard machine 1 implements the inventive method.

The paper machine or paperboard machine 1 has a wet section 20 with a dewatering apparatus 21, in which a fibrous material 2 is applied onto a long mesh 23 by a headbox 3. Headbox 3 is constructed as a dilution water headbox. Dilution water headbox 3 has along CD direction 15 of a fibrous web 5 a plurality of fibrous material outlet openings 4.

With the help of dewatering elements 16 there takes place a first dewatering step for fibrous material 2 in fibrous web 5 conveyed on long mesh 23. Dewatering elements 16 are constructed here as suction boxes 16. The embodiment shown includes two suction boxes 16, whose dewatering performance is zonally adjustable. The paper machine or paperboard machine 1 has further sections such as a drying section, a pressing section and also a reel, which for the sake of clarity are not shown. These sections can also contain zonally adjustable dewatering elements 16, such as, for example, segmented calender rolls (FIG. 1).

In MD direction 14 downstream from each dewatering element 16 and upstream from the first dewatering element 16 in MD direction 14 there are arranged water weight sensors 12 for measuring the dewatering of fibrous material 2 in the form of its water weight. MD direction 14 is indicated in FIG. 1 by an arrow. Water weight sensors 12 can be arranged directly in dewatering elements 16, for example they could be integrally constructed with elements 16.

Long mesh 23 is deflected and driven at the end receiving the fibrous material by way a breast roll 22. Fibrous web 5 lies on the upper side of long mesh 23 and is moved continuously by mesh 23 in MD direction 14 and hence away from dilution water headbox 3, whereby the fibrous material is dewatered continuously by way of dewatering elements 16. Here the dewatering takes place by gravitation and in addition by way of vacuum extraction through suction boxes 16.

Here fibrous web 5 includes two zones 6 and 7 (as shown in FIG. 2). Zones 6 and 7 extend respectively over half of the total transverse extension B of fibrous web 5. Fibrous web 5 could also include more than two zones 6 and 7, for example it could include as many zones as sections which can be adjusted in their dewatering performance or zones which exist on a suction box 16. Zones 6 and 7 extend in both MD direction 14 and CD direction 15. Here zones 6 and 7 extend over the entire longitudinal extension L of fibrous web 5. However they could also be constructed shorter. For example, each of zones 6 and 7 could be divided at least once in MD direction 14, thus creating at least four zones. Then there would be respectively two zones arranged side by side in CD direction 15 and assigned to one suction box. There could also be more, in particular substantially more than four zones which, adjacent to, or apart from, each other, follow each other in pairs in both MD direction 14 and CD direction 15.

The water weight sensors 12 are arranged in mutually offset position. They are arranged in an offset position in both MD direction 14 and CD direction 15. Here they are arranged on the bottom side of fibrous web 5. They could also be arranged above fibrous web 5. Water weight sensors 12 could also be available in sections of the paper machine or paperboard machine 1 other than wet section 20. They could also be available, for example in, or in the region of, the press or the drying section etc.

Water weight sensors 12 are arranged preferably in pairs in a mutually offset position fashion. Through the offset positioning there results, in particular with more than two sensors 12 per zone, a gapped arrangement of sensors 12. The arrangement of the sensors 12 displays a periodicity. The periodicity can also be described as a pattern. The periodic arrangement forms in both CD direction 15 and MD direction 14 a significant gapped pattern. The gapped line pattern in CD direction 15 and the gapped line pattern in MD direction 14 are arranged such that sensors 12 are mutually offset in pairs in both MD direction 14 and CD direction 15. Through the specific offset arrangement there result gapped one-dimensional sensor arrangements 61 or, as in this case, at least one multi-dimensional sensor arrangement 17 of water weight sensors 12 as shown in FIG. 3.

The dewatering of fibrous material 2 is monitored by measurements of the water weight in fibrous material 2 using at least two sensors 12 assigned to zone 6 and 7. On the basis of the water weight measurements the dewatering can be adapted to a defined dewatering curve 19 in MD direction 14. A dewatering curve is usually plotted in the unit “grams of water per square meter” (g/m2 H2O) over the entire length of fibrous web 5. This unit is also used for dewatering curve 19 in FIG. 3, which presents fibrous web 5 along its left side in MD direction 14. The term “on the basis of” is used here to designate a causal relationship between the measurement of the water weight on the one hand and the adaptation of the ACTUAL dewatering state of fibrous material 2 to the selectable or selected dewatering curve 19.

Dewatering apparatus 1 has at least two dewatering elements which are respectively zonally adjustable and are arranged mutually offset to each other in MD direction 14. Dewatering elements 16 are constructed here as suction boxes. The dewatering performance of dewatering elements 16 is zonally adjustable on the basis of the measurements taken by water weight sensors 12.

Water weight sensors 12 and dewatering elements 16 are arranged in alternating succession MD direction 14. Here there is at least one water weight sensor 12 arranged upstream from the first and downstream from the last dewatering element 16 looking in MD direction 14. Arranged per measurement point 18 in the first embodiment are, in concrete terms looking in MD direction 14, five water weight sensors 12 with gaps in mutually offset position in CD direction 15. Three one-dimensional sensor arrangements 13 are available. Together the sensor arrangements form one multi-dimensional sensor field 17.

The dewatering is zonally adjustable by at least one backward-coupled control circuit 9. The control circuit 9 has preferably at least one microprocessor 11.

The dewatering is, preferably in addition, zonally adjustable by at least one forward-coupled control circuit 8, in this case likewise with a microprocessor 11. There could be, albeit less preferably, only at least one forward-coupled control circuit 8, meaning dewatering apparatus 1 could also be constructed without a backward-coupled control circuit 9. For the sake of clarity the forward and/or backward coupling loops 10, the control circuits 8 and 9 and the at least one microprocessor 11 are not shown in FIG. 3.

Inventive features not presented in FIG. 3 are shown in FIG. 4, which presents a second embodiment of the present invention.

Dewatering elements 16 are available in both embodiments only in, or in the region of, wet section 20. However, dewatering elements 16 could also be arranged, in particular respectively in addition or solely, in at least one additional section of dewatering apparatus 1, such as in a steam blower box or in a press or in a headbox 3, in particular in a dilution water headbox 3.

The first embodiment has three one-dimensional sensor arrangements 13 which are offset in pairs in CD direction 15 and have five water weight sensors 12 each. Sensor arrangements 13 and hence their sensors 12 are also set apart from each other in MD direction 14. The result is therefore a very regular periodicity as a pattern of sensors 12. A different pattern or different periodicity of sensors 12 is implemented on the second embodiment, which is presented in FIG. 4.

On the second embodiment the first sensor arrangement 13 in MD direction 14 is equipped with two sensors 12 per zone 6 and 7. Sensors 12 of first sensor arrangements 13 in MD direction 14 are arranged, looking in MD direction 14, shifted rather to the left edge of fibrous web 5. This illustrates a left-gapped sensor arrangement 13.

The three sensors 12 per zone 6 and 7 of second sensor phalanx 13, meaning the one arranged between two suction boxes 16, are more narrowly gapped than the two sensors 12 of first sensor arrangement 13. The three sensors per zone 6 and 7 of second sensor phalanx 13 are arranged, in relation to CD direction 15, more centrally in their respective zone than the two sensors 12 of a zone in the first sensor arrangement 13. This illustrates a zonally center- and narrow-gapped second sensor arrangement 13.

A third sensor arrangement 13 is arranged in MD direction 14 downstream from second suction box 16. The arrangement is constructed, as far as the periodicity or pattern is concerned, like first sensor arrangement 13, meaning similarly gapped with regard to the sensor spacing. However, sensors 12 of third sensor arrangement 13 are arranged, looking in MD direction 14, shifted rather to the right edge of the fibrous web 5. This illustrates, in analogy with first sensor arrangement 13, of a right-gapped third sensor arrangement 13. Here sensors 12 of sensor arrangements 13 variously distributed in MD direction 14 form in turn a specific pattern in which the total number of sensors 12 is reduced compared to the first embodiment. This is owed in particular to the fact that the first and the third sensor arrangement 13 is constructed with rather wide gaps.

In both embodiments, the dewatering performance of dewatering element 16 in zone 6 and 7 is measured at a certain time by at least one water weight sensor 12. The measurement point 18 (see FIG. 4) of water weight sensor 12 in MD direction 14 is freely selectable. Similarly in both embodiments, at least one measurement point 18 looking in MD direction 14 there are at least two water weight sensors 12 per zone 6 and 7 arranged in mutually offset position in CD direction.

The measurements of at least a part of water weight sensors 12, which are arranged in an offset position in MD direction 14 and are assigned to zone 6 and 7, are averaged. This describes a blurring or slurring of the measurements. Similarly, the terms filtering and smoothing also apply for this calculation process. The averaging produces a slurred or blurred signal. In conjunction with the offset-periodic arrangement of the sensors arranged as a pattern it is possible to calculate the water curve (ACTUAL) from the averaged or filtered or smoothed signal. As a further consequence the ACTUAL curve can be adapted to the DESIRED curve of dewatering diagram 19.

The adjustment, in particular control, of the dewatering takes place with the involvement of at least one microprocessor 11. The averaging is performed likewise preferably with the help of at least one microprocessor. The result of such a calculation is presented in the form of a water weight total cross profile 24 of all the sensors 12 in FIG. 3 directly after the right-hand end of fibrous web 5. A more exact image of the dewatering characteristic in CD direction 15 and/or in MD direction 14 is determined in a favorable manner through a suitable interpolation of measurement values from offset water weight sensors 12.

As has now been made plausible, the dewatering apparatuses 1 of both embodiments implement the inventive method for adjusting, in particular controlling, the dewatering of a fibrous material 2 which is conveyed as a fibrous web that can be divided into at least two zones arranged side by side in CD direction 15. Characteristic of the inventive method is the fact that the dewatering of fibrous material 2 is adaptable to dewatering curve 19 defined in MD direction 14 on the basis of measurements of the water weight of fibrous material 2 taken by at least two water weight sensors 12 which are assigned to zone 6 and 7 and arranged preferably in pairs in mutually offset position in both MD direction 14 and CD direction 15.

Other embodiments of the inventive method or the inventive dewatering apparatus are conceivable and possible. For example, the patterns and/or the number of sensors could be configured differently. For the two embodiments presented in detail, use is made respectively of similar types of water weight sensors. Depending on the section equipped with water weight sensors it can make sense however to combine unlike water weight sensors. The calculation of measured values from water weight sensors of different types is also counterplated.

Through the specific gapped arrangement of the sensors in a periodic pattern it is possible to adapt the total number of sensors to the quality requirements on the one hand and to budget requirements on the other hand. Furthermore, because the sensors are gapped and periodically offset in all main directions they result in blurring of the calculation and hence in an exact adjustment, in particular control, of the dewatering that is not disturbed by statistical interference.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF REFERENCE NUMERALS

1 Dewatering apparatus

2 Fibrous material

3 Headbox

4 Fibrous material outlet openings

5 Fibrous web

6 Zone

7 Zone

8 Forward-coupled control circuit

9 Backward-coupled control circuit

10 Forward/backward coupling loop

11 Microprocessor

12 Water weight sensor

13 One-dimensional sensor arrangement

14 Machine running direction (MD direction)

15 Cross machine direction (CD direction)

16 Dewatering element

17 Multi-dimensional sensor arrangement

18 Measurement point

19 Dewatering curve

20 Wet section

21 Dewatering apparatus

22 Breast roll

23 Long mesh

24 Water weight total cross profile

L Longitudinal extension of the fibrous web

B Transverse extension of the fibrous web 

1. A dewatering apparatus for the adjustable controllable dewatering of a fibrous material which is conveyed as a fibrous web that is divided into at least two zones arranged side-by-side in a cross direction (CD), the dewatering apparatus comprising: a plurality of water weight sensors assigned to each of said at least two zones including a first water weight sensor and a second water weight sensor arranged in a mutually offset position in the CD direction, said plurality of water weight sensors being arranged in one of a one-dimensional and a multi-dimensional sensor arrangement, said plurality of water weight sensors being positioned and configured to carry out measurements of water weight of the fibrous material, the dewatering apparatus being configured to dewater the fibrous material dependent upon a dewatering curve defined in a machine direction (MD) and upon said measurements of water weight of the fibrous material.
 2. The dewatering apparatus of claim 1, further comprising a plurality of zonally adjustable dewatering elements in a wet section of the dewatering apparatus, said dewatering elements being at least one of a foil, a suction box, a pressing-on element in combination with an opposing mesh and a headbox, the dewatering apparatus being further configured to dewater the fibrous material in a zonally adjustable manner dependent upon said measurements taken by said water weight sensors.
 3. The dewatering apparatus of claim 2, wherein said water weight sensors and said dewatering elements are arranged in alternating succession in the MD direction.
 4. The dewatering apparatus of claim 3 further comprising at least one forward-coupled control circuit configured to zonally adjust the dewatering of the fibrous web.
 5. The dewatering apparatus of claim 4, wherein said at least one forward-coupled control circuit includes a microprocessor.
 6. The dewatering apparatus of claim 3 further comprising at least one backward-coupled control circuit configured to zonally adjust the dewatering of the fibrous web.
 7. The dewatering apparatus of claim 6, wherein said at least one backward-coupled control circuit includes a microprocessor.
 8. The dewatering apparatus of claim 2, wherein the dewatering apparatus includes at least one section having at least one of a steam blower box, a press, a headbox and a dilution water headbox, said dewatering elements being arranged in said at least one section.
 9. The dewatering apparatus of claim 2, wherein the dewatering apparatus is configured to influence a dewatering performance of said dewatering elements by way of at least one of an adjustable suction force, an adjustable layer thickness, an adjustable consistency of the fibrous material emerging from said headbox and an adjustable pressurization of the fibrous material by an opposing element and said mesh.
 10. The dewatering apparatus of claim 9, wherein said dewatering performance of said dewatering elements in one of said at least two zones is measured at a predetermined time by at least one of said plurality of water weight sensors, a measurement point of said at least one of said plurality of water weight sensors is freely selectable in the MD direction.
 11. The dewatering apparatus of claim 10, wherein at said measurement point looking in the MD direction there is arranged at least two of said plurality of water weight sensors in each of said at least two zones arranged in a mutually offset position in the CD direction.
 12. The dewatering apparatus of claim 1, wherein at least one of said plurality of water weight sensors is offset in the MD direction and is assigned to one of said at least two zones, said measurements of at least a part of said plurality of water weight sensors being averaged.
 13. The dewatering apparatus of claim 1, further comprising at lease one microprocessor configured to adjustably control the dewatering of the fibrous material.
 14. The dewatering apparatus of claim 1, wherein the dewatering apparatus is configured to provide an image of a dewatering characteristic in at least one of the CD direction and the MD direction by interpolation of the measurements of at least some of said plurality of water weight sensors.
 15. A method of adjustably controlling a dewatering of a fibrous material in a dewatering apparatus in one of a paper machine and a paperboard machine, the fibrous material being conveyed as a fibrous web that is divided into at least two zones arranged side-by-side in a cross machine direction (CD), the method comprising the steps of: measuring a water weight of the fibrous material by a plurality of water weight sensors which are assigned to one of said at least two zones; and adapting the dewatering of the fibrous material to a dewatering curve defined in a machine direction (MD) dependent upon said measuring step.
 16. The method of claim 15, wherein said plurality of water weight sensors include at least one pair of water weight sensors arranged in a mutually offset position in the CD direction. 